These same phrases also appear in the reverse tree (English from Portuguese) and when the translation was "voce tocou um elefante" without "em" it didn't seem to make sense to a lot of the native speakers. I read comments like: "What was he trying to do? Play the elephant as if it were a musical instrument?"
It looks like they're slowly changing all the translations where you touch something with your hand to "tocar em" in Portuguese.
I think it's in the article. Voice tocou em UM elefante- It kinda sounds weird to say did touch an elephant, unless maybe the questioner recognizes a certain smell. Have you ever touched an elephant (I've taken the liberty of adding ever, feels more idiomatic in English) makes more sense here.
Você tocou NO elefante- in this case the article tells us it's a particular elephant, and implies maybe a particular instance, so did you touch the elephant feels like a more natural translation.
"tocar" also could be "tocar um instrumento" - so this sounds to me like "Have you played (drums?) ON an elephant? :-) I'd leave out the "em" ...